Cannot use --lazy option on webpack-dev-server

[samueljseay]

Passing the --lazy flag to webpack-dev-server causes unexpected token at 'Cannot GET /webpack/manifest.json exception.

I've tried using the workarounds suggested in #58 just in case it was related, but it still breaks. You can reproduce this issue easily by adding the --lazy flag to the webpack command in the Procfile of https://github.com/mipearson/webpack-rails-demo

Is it possible for webpack-rails to support this functionality? If not, perhaps its worth documenting.